1. Field of the Invention
The present invention relates to a stabilized synthetic resin composition. Particularly, it relates to a synthetic resin composition which is stabilized against the deterioration caused by the action of heat or light by adding a specific cyclic phosphite and a hindered amine light stabilizer.
2. Description of the Prior Art
It is known that a synthetic resin such as polyethylene, polypropylene, ABS resin or polyvinyl chloride resin is unfit for long-term service, because it is deteriorated by the action of heat or light to cause discoloration or lowering in the mechanical strengths.
In order to prevent the above deterioration of a synthetic resin, many additives have been used alone or as various combinations. Particularly, a phosphite compound is known to have a relatively large effect upon the improvement in the heat resistance of a synthetic resin and the depression of the discoloration thereof. Such a phosphite compound includes triorganic phosphites such as trialkyl phosphites, triaryl phosphites and alkyl aryl phosphites and acid phosphites which are corresponding to the compounds obtained by replacing one of the organic groups of the organic triphosphite by a hydroxyl group. However, these phosphite compounds are unsatisfactory for practical use, because the stabilizing effect thereof is insufficient and the water resistance thereof is poor.
Among the organic phosphite compounds described above, a cyclic phosphite compound of a bisphenol is relatively excellent in stabilizing effect and water resistance. For example, U.S. Pat. No.3297631 discloses 2,2'-methylenebis(dialkylphenyl) phosphite. However, this compound is also poor in stabilizing effect and fails to provide satisfactory practical use.
Further, as compounds more desirable than the phosphite compounds described above, Japanese Patent Laid-Open No.100391/1979 discloses cyclic phosphites of o-bisphenol, while Japanese Patent Laid-Open Nos.114595/1982 and 103537/1983 disclose cyclic phosphites of 2,2'-bisphenol. However, these compounds also exhibit only an unsatisfactory stabilizing effect and are further disadvantageous in that the process for the preparation thereof is complicated. Accordingly, they have not been practically used as yet.
Meanwhile, in order to prevent a synthetic resin from deteriorating in the hue or lowering in the mechanical strengths caused by irradiation with light, ultraviolet absorbers such as benzophenone, benzotriazole, benzoate or cyanoacrylate or light stabilizers such as hindered amine have been used alone or as a mixture of two or more of them. However, many of these compounds stain a resin and are poor in the effect, so that the development of a more desirable stabilizer has been expected.
Among the compounds described above, hindered amine compounds having a tetramethylpiperidyl group have recently been noted, because they are non-staining and exhibit a relatively large effect upon the light stabilization of a synthetic resin. Therefore, many hindered amine compounds of such a type have been proposed. However, when such a hindered amine compound is used alone, the effect is insufficient, particularly unsatisfactory at all for uses wherein long-term resistance to heat and light is necessitated.
Further, Japanese Patent Laid-Open No.66551/1977 discloses that the resistance of a synthetic resin to heat and light is improved by using a combination of a hindered amine light stabilizer and one of various phosphites. However, such a combination does not give an effect satisfactory enough to be used practically, so that the development of a combination of stabilizers having a more desirable effect has been expected.